X-ray crystallography for the study of nickel and iron salicylaldimines

X-ray diffraction of single crystals has developed dramatically over the last century by combining fundamental theories of light, diffraction, and statistics to generate the complete, geometric structure of molecules. The quality of the resulting X-ray structure data are reported in R1 < 5%, wR2 < 12% and a goodness of fit value of one. This technique was applied specifically to the evaluation of the spin crossover (SCO) compound [Fe(salpm)2]BF4•0.5EtOH and how the molecule's geometry changed during a two-step thermal LS-HS conversion. The crystal structure was measured at 100, 175, 225, and 296 K to yield final R1 values of 0.047, 0.054, 0.051, and 0.058, respectively. The coordination bond lengths show the spin transitions occur between 100-175K at one crystallographically unique Fe and between 175-225K at the other Fe site. No strong long range interactions are found, suggesting a gradual spin transition. Reaction of Ni(N-alkyl-sal)2 complexes with Ni(NO3)2 form either nickel dimeric, [Ni(Rsal)(NO3)(MeOH)]2 or trinuclear complexes, Ni3(Rsal)4(NO3) 2. The binuclear complexes, with orthogonal bridging ligands, show overall ferromagnetic interactions. The crystal structures for Ni3(Rsal) 4(NO3)2 from methyl to benzyl were solved and indicate no steric restriction on formation for the series. The trinuclear compounds form an isosceles triangle of metal atoms with the isopropyl analog showing an overall antiferromagnetic interaction with J=+11.386 and J 23=-13.891. Lastly, xanthene spirolactam derivatives were structurally analyzed to determine binding modes for their selective and sensitive (μM) detection of metals Cr3+, Fe3+, Ni2+ , Co2+ and the nerve gas mimic, dichlorophosphate.